Pennington et a\: Assessing the precision of frequency distributions from trawl survey sample 



77 



well within the 95% confidence interval for R (Fig. 1 ). The 

 results of the simulations for the winter sur\'ey in 1999 

 were similar to those for 199.5 (Fig. 2). 



Bootstrapped estimates of the Q5'^A confidence intervals 

 for the estimated proportion of fish in each 5-cm length 

 bin for the 1995 and 1999 Barents Sea winter survey of 

 cod are shown in Figure .3. The inner brackets denote the 

 confidence intei-\-al based on the total number of fish ac- 

 tuallv measured and the outer brackets denote the confi- 



dence intervals if a ma.ximum of 10 fish were measured 

 per subsample. 



Discussion and conclusions 



For all the sui-veys e,\ammed. the effective sample size for 

 the survey length data was much smaller than the total 

 number offish measured. The average effective sample size 



